# Cyclotomic polynomial

From Citizendium

In algebra, a **cyclotomic polynomial** is a polynomial whose roots are a set of primitive roots of unity. The *n*-th cyclotomic polynomial, denoted by Φ_{n} has integer cofficients.

For a positive integer *n*, let ζ be a primitive *n*-th root of unity: then

The degree of is given by the Euler totient function .

Since any *n*-th root of unity is a primitive *d*-th root of unity for some factor *d* of *n*, we have

By the Möbius inversion formula we have

where μ is the Möbius function.